The scanning tunneling microscope is designed to obtain a sample image with atomic resolution from a tunneling current flowing between a probe tip and a sample. On the other hand, the atomic force microscope produces an image of a sample with atomic resolution from an atomic force exerted between a probe tip attached to the front end of a cantilever and the sample.
In this scanning probe microscope, the sample is often observed while maintained at cryogenic temperatures by a sample-cooling device. One major object of maintaining the sample at cryogenic temperatures is to reduce the effect of thermal vibrations of sample atoms, thereby enhancing the resolution of the atomic image. Another major object is to observe the physical characteristics of the sample at quite low temperatures.
The sample-cooling device is required to (1) be capable of cooling the sample down to cryogenic temperatures, (2) be capable of reaching cryogenic temperatures in a short time, and (3) consume only a small amount of refrigerant for the cooling per unit time.